Diamond Nanopillars Research Articles

Photonic-Cavity-Enhanced Laser Writing of Color Centers in Diamond.

Color centers in diamond have widespread utility in quantum technologies, but their creation process remains stochastic in nature. Deterministic creation of color centers in device-ready diamond platforms can improve the yield, scalability, and integration. Recent work using pulsed laser excitation has shown impressive progress in deterministically creating defects in bulk diamond. Here, we extend this laser-writing process into nanophotonic devices etched into diamond membranes, including nanopillars and photonic resonators with writing and subsequent readout occurring in situ at cryogenic temperatures. We demonstrate the optically driven creation of carbon vacancy (GR1) and nitrogen vacancy (NV) centers in diamond nanopillars and observe enhanced photoluminescence collection from them. We also fabricate bullseye resonators and leverage their cavity modes to locally amplify the laser-writing field, yielding defect creation with picojoule write-pulse energies 100 times lower than those typically used in bulk diamond demonstrations.

Toward Programmable Quantum Processors Based on Spin Qubits with Mechanically Mediated Interactions and Transport.

Solid-state spin qubits are promising candidates for quantum information processing, but controlled interactions and entanglement in large, multiqubit systems are currently difficult to achieve. We describe a method for programmable control of multiqubit spin systems, in which individual nitrogen-vacancy (NV) centers in diamond nanopillars are coupled to magnetically functionalized silicon nitride mechanical resonators in a scanning probe configuration. Qubits can be entangled via interactions with nanomechanical resonators while programmable connectivity is realized via mechanical transport of qubits in nanopillars. To demonstrate the feasibility of this approach, we characterize both the mechanical properties and the magnetic field gradients around the micromagnet placed on the nanobeam resonator. We demonstrate coherent manipulation of a spin qubit in the proximity of a transported micromagnet by utilizing nuclear spin memory and use the NV center to detect the time-varying magnetic field from the oscillating micromagnet, extracting a spin-mechanical coupling of 7.7(9)Hz. With realistic improvements, the high-cooperativity regime can be reached, offering a new avenue toward scalable quantum information processing with spin qubits.

Low-Cost Preparation of Diamond Nanopillar Arrays Based on Polystyrene Spheres.

Diamond nanopillar arrays can enhance the fluorescence collection of diamond color centers, playing a crucial role in quantum communication and quantum sensing. In this paper, the preparation of diamond nanopillar arrays was realized by the processes of polystyrene (PS) sphere array film preparation, PS sphere etching shrinkage control, tilted magnetron sputtering of copper film, and oxygen plasma etching. Closely aligned PS sphere array films were prepared on the diamond surface by the gas-liquid interfacial method, and the effects of ethanol and dodecamethylacrylic acid solutions on the formation of the array films were discussed. Controllable reduction of PS sphere diameter is realized by the oxygen plasma etching process, and the changes of the PS sphere array film under the influence of etching power, bias power, and etching time are discussed. Copper antietching films were prepared at the top of arrayed PS spheres by the tilted magnetron sputtering method, and the antietching effect of copper films with different thicknesses was explored. Diamond nanopillar arrays were prepared by oxygen plasma etching, and the effects of etching under different process parameters were discussed. The prepared diamond nanopillars were in hexagonal close-rowed arrays with a spacing of 800 nm and an average diameter of 404 nm, and the spacing, diameter, and height could be parametrically regulated. Raman spectroscopy and photoluminescence spectroscopy detection revealed that the prepared diamond nanopillar array still maintains polycrystalline diamond properties, with only a small amount of the graphite phase appearing. Moreover, the prepared diamond nanopillar array can enhance the photoluminescence of diamond color centers by approximately 2 times. The fabrication method of diamond nanopillar array structures described in this article lays the foundation for quantum sensing technology based on diamond nanostructures.

Tension–compression asymmetry in mechanical properties of diamond nanopillars: molecular dynamics simulations

Tension–compression asymmetry in mechanical properties of diamond nanopillars: molecular dynamics simulations

Shallow Silicon Vacancy Centers with Lifetime-Limited Optical Linewidths in Diamond Nanostructures.

The negatively charged silicon vacancy center (SiV-) in diamond is a promising, yet underexplored candidate for single-spin quantum sensing at sub-kelvin temperatures and tesla-range magnetic fields. A key ingredient for such applications is the ability to perform all-optical, coherent addressing of the electronic spin of near-surface SiV- centers. We present a robust and scalable approach for creating individual, ∼50 nm deep SiV- with lifetime-limited optical linewidths in diamond nanopillars through an easy-to-realize and persistent optical charge-stabilization scheme. The latter is based on single, prolonged 445 nm laser illumination that enables continuous photoluminescence excitation spectroscopy without the need for any further charge stabilization or repumping. Our results constitute a key step toward the use of near-surface, optically coherent SiV- for sensing under extreme conditions, and offer a powerful approach for stabilizing the charge-environment of diamond color centers for quantum technology applications.

Multicone Diamond Waveguides for Nanoscale Quantum Sensing.

The long-lived electronic spin of the nitrogen-vacancy (NV) center in diamonds is a promising quantum sensor for detecting nanoscopic magnetic and electric fields in various environments. However, the poor signal-to-noise ratio (SNR) of prevalent optical spin-readout techniques presents a critical challenge in improving measurement sensitivity. Here, we address this limitation by coupling individual NVs to optimized diamond nanopillars, thereby enhancing the collection efficiency of fluorescence. Guided by near-field optical simulations, we predict improved performance for tall (≥5 μm) pillars with tapered sidewalls. This is subsequently verified by fabricating and characterizing a representative set of structures using a newly developed nanofabrication process. We observe increased SNR for optimized devices, owing to improved emission collimation and directionality. Promisingly, these devices are compatible with low-numerical-aperture collection optics and a reduced tip radius, reducing experimental overhead and facilitating improved spatial resolution for scanning applications.

Physics of Complex Photonic Media and Metamaterials: feature issue introduction

We introduce the Optical Materials Express feature issue on the Physics of Complex Photonic Media and Metamaterials. This issue comprises a collection of nine manuscripts on the development, characterization, control, and applications of complex photonic media and metamaterials, including but not limited to metagratings, chiral metamirrors, diamond nanopillars, rotating metamaterials, and networks of random lasers.

Enhancing photon collection from single shallow nitrogen-vacancy centers in diamond nanopillars for quantum heterodyne measurements

The developments in quantum sensing protocols and nano-photonic waveguides are merged to improve the performance of single nitrogen-vancancy (NV) centers in nuclear magnetic resonance (NMR) sensing. Nanopillars are designed with NV centers placed approximately 5 nm below the top facet and fabricated through a simple procedure, suitable for mass production. Fluorescence intensities from these nanopillars are 3.5 times greater than that of single shallow NV centers embedded in unstructured flat diamond. Quantum heterodyne measurements of an alternating magnetic field are performed with these nanopillars and evidence of improved peak clarity in the frequency spectrum is shown.

Nanoscale Vector Magnetometry with a Fiber‐Coupled Diamond Probe

AbstractA nanoscale vector magnetometer is demonstrated by integrating a microfabricated diamond probe with a nanopillar on top of a single‐mode optical fiber. Based on the recently developed self‐aligned patterning techniques, ≈80 nitrogen vacancies are concentrated at a 100 nm2 area at the center of nanopillars to maximize the excitation and collection efficiencies. The spatial resolution of such a fiber‐coupled diamond magnetometer can reach 100 nm for the first time with a sensitivity of 11.27 µT/ for DC magnetic field sensing. In addition, the probe can provide deterministic oriented diamond nanopillars for simplified vector magnetometry. This fiber‐coupled diamond probe is applied to demonstrate the magnetic field imaging of charged electrodes in a confined box. These results mark a decisive step toward fiber‐based applications with nanoscale vector magnetometry capabilities.

Spectroscopic Study of N- V Sensors in Diamond-Based High-Pressure Devices

High-pressure experiments are crucial in modern interdisciplinary research fields such as engineering quantum materials, yet local probing techniques remain restricted due to the tight confinement of the pressure chamber in certain pressure devices. Recently, the negatively charged nitrogen-vacancy (N-$V$) center has emerged as a robust and versatile quantum sensor in pressurized environments. There are two popular ways to implement N-$V$ sensing in a diamond anvil cell (DAC), which is a conventional workhorse in the high-pressure community: create implanted N-$V$ centers (IN-$V\mathrm{s}$) at the diamond anvil tip or immerse N-$V$-enriched nanodiamonds (NDs) in the pressure medium. Nonetheless, there are limited studies on comparing the local stress environments experienced by these sensor types as well as their performances as pressure gauges. In this work, by probing the N-$V$ energy levels with the optically detected magnetic resonance (ODMR) method, we experimentally reveal a dramatic difference in the partially reconstructed stress tensors of IN-$V\mathrm{s}$ and NDs incorporated in the same DAC. Our measurement results agree with computational simulations, concluding that IN-$V\mathrm{s}$ perceive a more nonhydrostatic environment dominated by a uniaxial stress along the DAC axis. This provides insights on the suitable choice of N-$V$ sensors for specific purposes and the stress distribution in a DAC. We further propose some possible methods, such as using NDs and diamond nanopillars, to extend the maximum working pressure of quantum sensing based on ODMR spectroscopy, since the maximum working pressure could be restricted by nonhydrostaticity of the pressure environment. Moreover, we explore more sensing applications of the N-$V$ center by studying how pressure modifies different aspects of the N-$V$ system. We perform a PL study using both IN-$V\mathrm{s}$ and NDs to determine the pressure dependence of the zero-phonon line, which helps developing an all-optical pressure sensing protocol with the N-$V$ center. We also characterize the spin-lattice relaxation (${T}_{1}$) time of IN-$V\mathrm{s}$ under pressure to lay a foundation for robust pulsed measurements with N-$V$ centers in pressurized environments.

Neuronal growth on high-aspect-ratio diamond nanopillar arrays for biosensing applications

Monitoring neuronal activity with simultaneously high spatial and temporal resolution in living cell cultures is crucial to advance understanding of the development and functioning of our brain, and to gain further insights in the origin of brain disorders. While it has been demonstrated that the quantum sensing capabilities of nitrogen-vacancy (NV) centers in diamond allow real time detection of action potentials from large neurons in marine invertebrates, quantum monitoring of mammalian neurons (presenting much smaller dimensions and thus producing much lower signal and requiring higher spatial resolution) has hitherto remained elusive. In this context, diamond nanostructuring can offer the opportunity to boost the diamond platform sensitivity to the required level. However, a comprehensive analysis of the impact of a nanostructured diamond surface on the neuronal viability and growth was lacking. Here, we pattern a single crystal diamond surface with large-scale nanopillar arrays and we successfully demonstrate growth of a network of living and functional primary mouse hippocampal neurons on it. Our study on geometrical parameters reveals preferential growth along the nanopillar grid axes with excellent physical contact between cell membrane and nanopillar apex. Our results suggest that neuron growth can be tailored on diamond nanopillars to realize a nanophotonic quantum sensing platform for wide-field and label-free neuronal activity recording with sub-cellular resolution.

High-Q Fano resonances in diamond nanopillars

We report on the optical behaviour of a nanostructured diamond surface on a glass substrate. The numerical model reveals that a simple geometrical pattern sustains Fano-like resonances with a Q-factor as high as 3.5 · 105 that can be excited by plane waves impinging normally on the surface. We show that the geometrical parameters of the nanopillars affect both the resonant frequency and the line shape. The nanostructured surface can be straightforwardly used as a refractive index sensor with high sensitivity and linearity. Our findings show that diamond-based meta-surfaces are a valuable nanophotonic platform to control light propagation at the nanoscale, enabling large field enhancement within the nanoresonators that can foster both linear and nonlinear effects.

Templated Synthesis of Diamond Nanopillar Arrays Using Porous Anodic Aluminium Oxide (AAO) Membranes

Diamond nanostructures are mostly produced from bulk diamond (single- or polycrystalline) by using time-consuming and/or costly subtractive manufacturing methods. In this study, we report the bottom-up synthesis of ordered diamond nanopillar arrays by using porous anodic aluminium oxide (AAO). Commercial ultrathin AAO membranes were adopted as the growth template in a straightforward, three-step fabrication process involving chemical vapor deposition (CVD) and the transfer and removal of the alumina foils. Two types of AAO membranes with distinct nominal pore size were employed and transferred onto the nucleation side of CVD diamond sheets. Subsequently, diamond nanopillars were grown directly on these sheets. After removal of the AAO template by chemical etching, ordered arrays of submicron and nanoscale diamond pillars with ~325 nm and ~85 nm diameters were successfully released.

Controllable preparation of single-crystal diamond nanopillar clusters by metal cyclic dewetting process

Diamond nanopillars can effectively improve the spontaneous emission efficiency and coupling-out efficiency of diamond-color-center single-photon sources. In this paper, a low-cost and controllable method for preparing diamond nanopillar clusters is proposed. By choosing the crystal planting method and adjusting the methane concentration of the grown diamonds, isolated single-crystal diamond particles with a flat surface were prepared. Etching masks with individually controllable diameters and spacings were prepared through the cyclic deposition and dewetting of metal films on the surface of microcrystalline diamond particles. Using inductively coupled reactive ion etching technology, diamond nanopillar clusters were prepared through oxygen plasma etching. The nanopillars were uniform in diameter and densely arranged. The single-crystal properties of the diamond nanopillars and their enhancement effect on the photoluminescence of diamond color centers were confirmed through the analysis of Raman and photoluminescence spectra. The results provide a foundation for the deviceization of diamond-color-center single-photon sources.

Correction: Radtke et al. Plasma Treatments and Light Extraction from Fluorinated CVD-Grown (400) Single Crystal Diamond Nanopillars. C 2020, 6, 37

The authors would like to update the XPS spectrum in Figure 3c [...]

Scalable and Tunable Diamond Nanostructuring Process for Nanoscale NMR Applications.

Nanostructuring of a bulk material is used to change its mechanical, optical, and electronic properties and to enable many new applications. We present a scalable fabrication technique that enables the creation of densely packed diamond nanopillars for quantum technology applications. The process yields tunable feature sizes without the employment of lithographic techniques. High-aspect-ratio pillars are created through oxygen-plasma etching of diamond with a dewetted palladium film as an etch mask. We demonstrate an iterative renewal of the palladium etch mask, by which the initial mask thickness is not the limiting factor for the etch depth. Following the process, 300–400 million densely packed 100 nm wide and 1 μm tall diamond pillars were created on a 3 × 3 mm2 diamond sample. The fabrication technique is tailored specifically to enable applications and research involving quantum coherent defect center spins in diamond, such as nitrogen-vacancy (NV) centers, which are widely used in quantum science and engineering. To demonstrate the compatibility of our technique with quantum sensing, NV centers are created in the nanopillar sidewalls and are used to sense 1H nuclei in liquid wetting the nanostructured surface. This nanostructuring process is an important element for enabling the wide-scale implementation of NV-driven magnetic resonance imaging or NV-driven NMR.

Simulations of plasticity in diamond nanoparticles showing ultrahigh strength

We use molecular dynamics (MD) simulations to deform single crystal spherical carbon nanoparticles (NP), 4–45 nm diameter, with a hard, flat indenter, compressing along the [001] direction. There is no clear amorphization nor phase change in the NP, but there is significant deformation, with bent crystalline planes, and many atoms that retain sp3 coordination, but are no longer recognized as having diamond structure by different structure-identification methods. Machine-learning is used to improve diamond-structure identification. The NP deforms laterally, and volumetric strain is ~0.1 when the uniaxial strain is ~0.5. Poisson's ratio increases with strain, and the elastic limit is reached at 0.2–0.3 strain, at a contact pressure of ~150 GPa. For NPs above 5 nm, dislocations appear and are mostly (1/2)<110>{111} full dislocations, with a few partial dislocations for larger nanoparticles, without twinning. These results agree with the recent observation of plastic deformation in diamond nanopillars. Small NP display elastic modulus, yield stress and hardness increasing with NP size, but NPs with diameter larger than 25 nm display an approximately constant dislocation and dislocation junction density, which leads to a plateau in the hardness versus NP size, at ~150 GPa, close to bulk diamond. Diamond nanoparticles could provide high strength thin coatings, lighter than full-density nanotwinned diamond but with nearly the same strength.

Optical and Spin Properties of NV Center Ensembles in Diamond Nano-Pillars.

Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.

Room-temperature plasticity in diamond

In spite of extremely high strength and hardness, the property of brittleness is tightly linked to diamond. In the deformation of diamond at room temperature, the plasticity of the diamond is normally considered hard to occur because of the domination of catastrophic brittle fracture. Herein, we employed in-situ transmission electron microscopy to reveal the diamond room-temperature plastic behavior, and compared it with a recent report (Adv. Mater. 2020, 1906458) on transformation-induced room-temperature plasticity of diamond nanopillars. Our present in-situ uniaxial compression tests in sub-micron-sized diamond pillars indicate that the plasticity in diamond is carried out by dislocations slipping instead of phase transformation and the initiation of plasticity highly depends on the stress state. On the other hand, we noted that a high proportion of amorphous surface layer in the diamond pillars with a diameter of less than 20 nm may be a significant factor leading to the plasticity.

Plasma Treatments and Light Extraction from Fluorinated CVD-Grown (400) Single Crystal Diamond Nanopillars

We investigate the possibilities to realize light extraction from single crystal diamond (SCD) nanopillars. This was achieved by dedicated 519 nm laser-induced spin-state initiation of negatively charged nitrogen vacancies (NV−). We focus on the naturally-generated by chemical vapor deposition (CVD) growth of NV−. Applied diamond was neither implanted with 14N+, nor was the CVD synthesized SCD annealed. To investigate the possibility of light extraction by the utilization of NV−’s bright photoluminescence at room temperature and ambient conditions with the waveguiding effect, we have performed a top-down nanofabrication of SCD by electron beam lithography (EBL) and dry inductively-coupled plasma/reactive ion etching (ICP-RIE) to generate light focusing nanopillars. In addition, we have fluorinated the diamond’s surface by dedicated 0 V SF6 ICP plasma. Light extraction and spin manipulations were performed with photoluminescence (PL) spectroscopy and optically detected magnetic resonance (ODMR) at room temperature. We have observed a remarkable effect based on the selective 0 V SF6 plasma etching and surprisingly, in contrast to literature findings, deactivation of NV− centers. We discuss the possible deactivation mechanism in detail.